The present invention relates to a hub unit for supporting a wheel shaft, which is utilized for supporting a wheel of a vehicle rotatively relative to a suspension system.
Wheels of a vehicle are supported on the suspension system by means of hub units for supporting wheels. FIG. 8 shows one example of a hub unit for supporting a wheel described in U.S. Pat. No. 5,490,732. A hub unit 1 for supporting a wheel comprises a shaft member 2, a pair of inner rings 3a, 3b, an outer ring 4, and a plurality of rolling elements 5, 5. A flange (a first flange) 6 for supporting a wheel is formed along the outer peripheral surface of outer-edge portion of the shaft member 2 (here the expression xe2x80x9cout or outsidexe2x80x9d designates a direction toward the outside of the vehicle in a widthwise direction when the hub unit is mounted on the vehicle, that is, a leftward direction in FIG. 8, and in contrast, an expressionxe2x80x9cin or insidexe2x80x9d designates a direction toward the center of the vehicle in the widthwise direction, that is, a rightward direction in FIG. 8.). A stepped portion 7 is formed along the base of the flange 6 in the vicinity of the axial center of the axial member 2.
The pair of inner rings 3a, 3b are provided and fitted around the outer surface of the axial member 2 which ranges from the middle portion to the inner end of the axial member. The outer side surface of the inner ring 3a abuts a vertical surface of the stepped portion 7, and the outer side surface of the inner ring 3b abuts the inner side surface of the inner ring 3a. A cylindrical portion 8 is formed in the inner end surface of the shaft member 2. A caulked portion 9 is formed by bending, in a diametrical outward direction, the edge of the cylindrical portion 8 which protrudes toward the inside beyond the inner end surface of the inner ring 3b. The pair of inner rings 3a, 3b are sandwiched between the vertical surface of the stepped portion 7 and the caulked portion 9.
The plurality of rolling elements 5, 5 are provided between a pair of outer (first and second) raceways 10, 10 formed along the inner peripheral surface of the outer ring 4 and a pair of inner (first and second) raceways 11, 11 formed respectively along the outer peripheral surfaces of the inner rings 3a, 3b. Although balls are used as the rolling elements 5, 5 in an illustrated example, tapered rollers may also be used as the rolling elements for a heavy hub unit for supporting a vehicle wheel. Alternatively, the (first) inner raceway formed adjacent to the flange 6 may be directly formed along the outer peripheral surface of the shaft member 2, and the outer inner ring 3a may be omitted in some cases. In such a case, the stepped portion 7 is formed in an inner position relative to the inner ring 3a shown in FIG. 8.
The foregoing hub unit 1 is locked to the vehicle by securing the outer wheel 4 to the suspension system through use of an outwardly extending flanged mount (a second flange) 12 formed along the outer peripheral surface of the outer wheel 4, and by fastening the wheel to the flange 6. As a result, the wheel can be rotatively secured to the suspension system.
In the case of the conventional construction shown in FIG. 8, the caulked portion 9 is susceptible to damage such as cracks when being formed in order to fixedly fit the inner rings 3a, 3b on the shaft member 2. Further, at the time of formation of the caulked portion 9, force is exerted, in a diametrical outward direction, on the inner peripheral surface of the inner ring 3b adjoining the caulked portion 9. In short, in the case of the conventional construction, for the purpose of forming the caulked portion 9, the cylindrical portion 8 is formed in the inner end face of the shaft member 2 in such a way that the inner and outer peripheral surfaces of the cylindrical portion 8 become concentric with each other in axial direction of the shaft member. Since the outer and inner peripheral surfaces of the shaft member are formed into mere cylindrical surfaces which are concentric with each other, the cylindrical portion 8 is formed with uniform thickness over its entire length. Such a construction requires great force to produce the caulked portion 9 by caulking the protruding edge of the cylindrical portion 8, rendering the caulking operation laborious. Further, the caulking operation entails exertion of great tensile force on the leading edge of the caulked portion 9, rendering the caulked portion susceptible to damage.
Since great force is exerted on the leading edge of the caulked portion when the caulked portion is formed by caulking, the force exerted on the internal peripheral surface of the inner ring 3b from the caulked portion is also increased correspondingly. Although not to a greater extent, the diameter of the inner ring 3b is slightly changed. If there is an increase in the amount of change in the diameter of the inner ring, there arises a risk of the inner ring 3b being subjected to damage such as cracks, and a risk of a change in the diameter of the inner raceways 11, 11 formed along the outer peripheral surface of the inner ring 3b or of deterioration of geometrical accuracy (e.g., roundness or the degree of accuracy of a cross-sectional profile) of the inner ring. This in turn makes it laborious to maintain at an optimum value the preload imparted to the rolling elements 5, 5 interposed between the inner raceways 11, 11 formed along the outer peripheral surface of the inner ring 3b and the outer raceways 10, 10 facing the inner raceways 11, 11, posing the risk of difficulty of ensuring the durability of the hub unit 1.
The hub unit according to the present invention has been conceived in view of the foregoing problems, and an object of the present invention is to prevent a caulked portion from being subjected to damage such as cracks when an inner ring is fixed, as well as to prevent a change in the inner diameter of the inner ring or the diameter of inner raceways formed along the outer periphery of the inner ring, which would otherwise caused by a caulking operation to such an extent as to pose practical problem.
Similar to the conventional hub unit mentioned previously, a hub unit for supporting a wheel of a vehicle according to the present invention also includes: a shaft member having a first flange which is formed at one end of the shaft member on the outer peripheral surface of the same; a first inner raceway which is formed directly on the outer peripheral surface of the intermediate portion of the shaft member or indirectly on the same by way of an inner raceway separated from the shaft member; a stepped portion which is formed in the vicinity of the other end of the shaft member and which has an outer diameter smaller than that of the area of the shaft member where the first inner raceway is formed; an inner ring which has a second inner raceway formed on the outer peripheral surface thereof and which is fitted around the stepped portion; an outer ring which has a first outer raceway formed on the internal peripheral surface thereof so as to face the first inner raceway, a second outer raceway formed on the same so as to face the second inner raceway, and a second flange formed on the outer peripheral surface thereof; and a plurality of rolling elements which are interposed between the first inner raceway and the first outer raceway and between the second inner raceway and the second outer raceway. The hub unit of the present invention further comprises a caulked portion formed by caulking and spreading in a diametrical outward direction a portion of a cylindrical portion which is formed on the other end of the shaft member and which extends beyond at least the inner ring fitted around the stepped portion. The caulked portion presses the inner ring fitted around the stepped portion toward the end face of stepped portion, thereby fixedly fastening the inner ring fitted around the stepped portion to the shaft member. Particularly, the hub unit according to the present invention is characterized by the feature that the cylindrical portion has a smaller thickness toward the leading end of the cylindrical portion before it is caulked and spread in the diametrical outward direction, and the thickness of the caulked portion, which is formed by caulking and spreading in the diametrical outward direction the cylindrical portion and which presses the end face of the inner ring fitted around the stepped portion, is gradually reduced toward the leading end of the caulked portion in comparison with the thickness of the base of the cylindrical portion.
More preferably, the hub unit according to the present invention has one or both of the following requirements {circle around (1)} and {circle around (2)}.
{circle around (1)} The opening formed on the other end of the ring has a chamfer which has a circular-arc cross section and which connects the inner end flat surface of the inner ring to the inner peripheral and cylindrical surface of the inner ring.
The outer peripheral edge of the caulked portion is placed at an inner position in a diametrically inward direction relative to the point of intersection between the outer peripheral edge of the chamfer and the inner peripheral edge of the inner end surface of the inner ring.
{circle around (2)} A first axial position is set at a point which is spaced away from the inner end surface of the inner ring toward the center axis of the shaft member by a distance which is 1.26 times the width to be caulked equal to half of the difference between the outer diameter of the caulked portion and the inner diameter of the inner ring. Further, the inner most end of the inner peripheral surface used for forming the caulked portion is taken as a second axial position. A third axial position is set at a point on the side surface close to the inner end surface of the inner ring among the surfaces of the inner raceway formed along the outer peripheral surface of the inner ring. In a state in which the caulked portion is formed, the second axial position is placed at a position, in the axial direction of the shaft member, between the first axial position and the third axial position.
The operation of the hub unit for supporting a vehicle wheel having the foregoing structure according to the present invention is the same as that of the conventional hub unit; that is, the hub unit rotatively supports a wheel with respect to a suspension system.
Particularly, in the case of the hub unit according to the present invention, since the thickness of the cylindrical portion used for forming the caulked portion is gradually reduced toward the leading edge, excessively great force is not required to form the caulked portion. Accordingly, the caulked portion is protected from damage such as cracks, which would otherwise be caused when the caulked portion is machined. Further, it is possible to prevent force, which would otherwise change the diameter of the inner ring fitted to the shaft member by the caulked portion such an extent as to affect the preload exerted on the inner ring or the durability of the inner ring such as the rolling fatigue life of the inner ring.
In a case where the hub unit satisfies the requirement {circle around (1)}, the outer peripheral edge of the caulked portion can be effectively protected from imperfections such as cracks, burrs, or underfill.
Further, in a case where the hub unit satisfies the requirement {circle around (2)}, no clearance arises between the outer peripheral surface of the caulked portion and the inner peripheral surface of the inner ring, and the supporting strength of the inner ring imparted by the caulked portion is ensured. Further, the deformation of the inner raceway is also prevented.